This invention generally relates to methods and apparatus for manufacturing slider-operated flexible zippers for use in reclosable pouches, bags or other packages of the type in which perishable material, such as foodstuff, are stored.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zippers include a pair of interlockable fastener elements, or profiles, that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc.
Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction.
Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures. The first profiled structure comprises an interlocking element on a surface directed toward the second profiled structure and an integral base directed away from the second profiled structure. Likewise, the second profiled structure comprises an interlocking element on a surface directed toward the first profiled structure and an integral base directed away from the first profiled structure. Additionally, portions of the two profiled structures form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other.
One of the important features of such reclosable fastener assemblies are the end stops, which prevent the slider from falling off the end of the fastener when the slider reaches the end of the fastener. End stops have taken on various configurations, such as, for example, riveted end clamps such as those described in U.S. Pat. Nos. 5,067,208 and 5,161,286; transverse end stops made from molten material of the fastener strips, as described in U.S. Pat. No. 5,088,971; reciprocating anvils, as described in U.S. Pat. No. 5,131,121; tubular end stops, as described in U.S. Pat. No. 5,405,478; a window structure combined with sealed zipper ends, as described in U.S. Pat. No. 5,442,837; or plastic end clips fused to the zipper as described in U.S. Pat. No. 5,448,807.
U.S. Pat. No. 5,950,285 discloses a reclosable bag having end stops that prevent a slider from moving beyond the end of the zipper when the slider reaches either the closed or fully open position. The end stops are formed from the material of the zipper profiles and xe2x80x9crise verticallyxe2x80x9d from the zipper to block and prevent further movement of the slider. The end stops are formed by first aligning together the opposing profiles at an end stop area proximate to an end of the bag, and then fusing the zipper profiles at the end stop area to provide a vertical structure for preventing movement of the slider past the ends of the zipper, while at the same time keeping the lower corners or rails of the zipper parts intact. Preferably, the profiles are fused by directing ultrasonic energy to the end stop area.
Consumers are provided with bulk quantities of various commodities, such as food products, that are marketed in reclosable packages having slider-operated zippers. Form/fill/seal machines are used to form a reclosable package having an opening for filling with product, filling the formed package with product and then sealing the opening to form the final product. Automated production lines using form/fill/seal machines of many different types are prevalent. Naturally, the production capacity of any facility is a function of the speed of the production line. Thus there is a constant need for innovations that will speed up the production line. Manufacturers of food products and other commodities are concerned with forming, filling and sealing a reclosable package as quickly and economically as possible.
Although improvements have been made in the art of plastic welding and joining, manufacturers of consumer products employing high-speed production techniques are continually seeking improved package forming methods and equipment. One area in which improvements in productivity have been sought is in the formation of the end stop that limits the travel of a slider or clip traveling along tracks or rails of a zipper or fastener. Any reduction in the time needed to form these and other package features can result in substantial cost savings.
In the past, heat conduction and ultrasonic sealing techniques have been used to deform or crush the end sections of a zipper into shapes capable of serving as slider end stops. More recently, slider end stops have been sculpted using ultrasonic sealing or welding techniques, which afford improved control over the size and shape of the end stops as compared to the results attainable using conduction heat sealing.
From a manufacturing standpoint, it is desirable to reduce the dwell time involved to melt and shape the end stop, thereby enhancing the overall efficiency of the package manufacturer. The larger the mass of thermoplastic zipper material that needs to be melted and shaped, the longer the dwell time of the package during the ultrasonic stomping operation. A longer dwell time during ultrasonic stomping in turn can reduce the speed of the form/fill/seal machine. Thus there is a need for innovations directed to speeding up the operation of ultrasonically stomping slider end stops on zippers.
The invention is directed to a method and an apparatus for ultrasonically stomping slider end stops on flexible zipper structures.
One aspect of the invention is an ultrasonic welding assembly comprising a horn and an anvil, wherein the horn comprises two prongs separated by a gap. Each prong comprises an end surface confronting the anvil, each end surface having at least a portion that is flat, the flat portions being generally coplanar.
Another aspect of the invention is a method for forming slider end stops on a zipper tape that comprises first and second interlockable zipper parts, the method comprising the following steps: (a) transmitting sufficient ultrasonic wave energy into first and second areas of the zipper tape to cause the first and second interlocked zipper parts to deform and fuse in the first and second areas, the first and second areas being separated by a gap; and (b) applying sufficient heat and pressure onto a third area of the zipper tape to cause the interlocked zipper parts to deform and fuse in the third area, at least part of the third area being located between the first and second areas in the gap.
Yet another aspect of the invention is a system for forming slider end stops on a zipper tape that comprises first and second interlockable zipper parts, the system comprising: an ultrasonic welding apparatus configured to transmit sufficient ultrasonic wave energy into first and second areas of the zipper tape to cause the first and second interlocked zipper parts to deform and fuse in the first and second areas, the first and second areas being separated by a gap; and a conduction heat sealing apparatus configured to apply sufficient heat and pressure onto a third area of the zipper tape to cause the interlocked zipper parts to deform and fuse in the third area, at least part of the third area being located between the first and second areas in the gap.
A further aspect of the invention is a method for forming slider end stops, comprising the following steps: advancing a web of packaging film material having a zipper tape joined thereto to a first station; at the first station, ultrasonically stomping the zipper tape in first and second areas, the first and second areas being separated by a gap; advancing the web by one package width in a lengthwise direction of the zipper tape so that the gap is in register with a second station; and at the second station, conduction heat sealing in a third area that lies at least partly in the gap between the first and second areas and includes a contiguous strip that extends generally transverse to the lengthwise direction, a portion of the zipper tape within the third area being deformed and portions of the packaging film material within the third area being joined to form a seal having a predetermined width.
Yet another aspect of the invention is a system for forming packages having slider-operated zippers, comprising first and second stations having respective registration points spaced at a distance equal to one or more package widths along a machine direction, wherein the first station comprises an ultrasonic welding apparatus configured to ultrasonically stomp a zipper tape in first and second areas spaced in the machine direction, the first and second areas being separated by a gap; and the second station comprises conduction heat sealing apparatus configured to heat seal packaging film material in a third area that lies at least partly in the gap between the first and second areas and includes a contiguous strip that extends generally transverse to the machine direction, a portion of the zipper tape within the third area being deformed and portions of the packaging film material within the third area being joined to form a seal having a predetermined width.
Other aspects of the invention are disclosed and claimed below.